WO2015033090A1 - Mesure de la charge d'une particule - Google Patents

Mesure de la charge d'une particule Download PDF

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Publication number
WO2015033090A1
WO2015033090A1 PCT/GB2014/000347 GB2014000347W WO2015033090A1 WO 2015033090 A1 WO2015033090 A1 WO 2015033090A1 GB 2014000347 W GB2014000347 W GB 2014000347W WO 2015033090 A1 WO2015033090 A1 WO 2015033090A1
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Prior art keywords
particle
determining
velocity
velocity component
calibration
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PCT/GB2014/000347
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English (en)
Inventor
Benjamin Mark Glossop
Robert Vogel
Eva WEATHERALL
Martin David Jones
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Izon Science Limited
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Application filed by Izon Science Limited filed Critical Izon Science Limited
Priority to EP14789858.9A priority Critical patent/EP3042179B1/fr
Priority to CN201480048308.1A priority patent/CN105705934B/zh
Priority to US14/916,405 priority patent/US10429347B2/en
Publication of WO2015033090A1 publication Critical patent/WO2015033090A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • G01N27/447—Systems using electrophoresis
    • G01N27/44756—Apparatus specially adapted therefor
    • G01N27/44791—Microapparatus
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/1031—Investigating individual particles by measuring electrical or magnetic effects
    • G01N15/12—Investigating individual particles by measuring electrical or magnetic effects by observing changes in resistance or impedance across apertures when traversed by individual particles, e.g. by using the Coulter principle
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/1031—Investigating individual particles by measuring electrical or magnetic effects
    • G01N15/12—Investigating individual particles by measuring electrical or magnetic effects by observing changes in resistance or impedance across apertures when traversed by individual particles, e.g. by using the Coulter principle
    • G01N15/131—Details
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • G01N27/4163—Systems checking the operation of, or calibrating, the measuring apparatus
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • G01N27/447—Systems using electrophoresis
    • G01N27/44704—Details; Accessories
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
    • G01R29/24—Arrangements for measuring quantities of charge
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/1031—Investigating individual particles by measuring electrical or magnetic effects
    • G01N15/12—Investigating individual particles by measuring electrical or magnetic effects by observing changes in resistance or impedance across apertures when traversed by individual particles, e.g. by using the Coulter principle
    • G01N15/13—Details pertaining to apertures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N2015/0003—Determining electric mobility, velocity profile, average speed or velocity of a plurality of particles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N2015/1027—Determining speed or velocity of a particle

Definitions

  • the invention relates to a method for measuring the charge of particles, in particular the surface charge of nanometre to micron sized particles suspended in a fluid.
  • the invention extends to apparatus for use in the above method, and to a computer program for use with such apparatus, for carrying out the above method.
  • the surface charge of objects in the nanometre and micron range is a key factor in their stability and general reactivity.
  • Surface charge and changes in surface charge can also be used to detect and quantify the presence of specific targets in a sample.
  • the ability to accurately measure the surface charge of objects is therefore important for a range of users from industrial (e.g. paint, ink and coating manufacture) through to pharmaceutical (e.g. vaccine QA) and scientific research (e.g. developing nanomedicines and specific molecular diagnostic tests).
  • Dynamic Light Scattering Phase Analysis Light Scattering- Quasi Electric Light Scattering.
  • Dynamic Light Scattering is used to measure particle and molecule size. This technique measures the diffusion of particles moving under Brownian motion, and converts this to size and a size distribution using the Stokes-Einstein relationship.
  • Micro-electrophoresis is used to measure the zeta potential or surface charge of particles.
  • an electric field is applied to a solution of molecules or a dispersion of particles, which then move with a velocity related to their zeta potential.
  • This velocity is measured using a laser interferometric technique (Phase Analysis Light Scattering or PALS).
  • PALS Phase Analysis Light Scattering
  • a further limitation of DLS analysis is that the average size distribution of a mixed population of particles is artificially skewed towards the larger particles, which scatter so much light that they can obscure smaller particles.
  • NTA Nanoparticle Tracking Analysis
  • D t speed of motion
  • D t diffusion coefficient
  • NTA non-invasive filtration rate
  • complex algorithms are applied to calculate the particle size and charge, and if the input settings are incorrect or not known the answer can be significantly erroneous. Additionally, compensation factors also need to be applied to balance both electro-osmotic flow and convection due to laser heating effects.
  • Vogel (Vogel, R., et al., "A Variable Pressure Method for Characterizing Nanoparticle Surface Charge Using Pore Sensors”. Analytical Chemistry, 2012. 84(7): p. 3125-3131.) describes one such application where sample particles are placed on both sides of the nanopore, and the pressure applied across a nanopore is adjusted until the flow of particles reverses direction. The applied pressure required to reach this "inversion point" is used as a measure of electrophoretic mobility. At the inversion point, the time it takes for particles to translocate the pore tends towards infinity, so translocation duration can also be used as an indicator.
  • the main limitations of these methods are that they are ensemble methods (not particle by particle), and that they are time- consuming as they require the adjusting of many parameters and many measurements. Additionally, with the pressure-sweep method in particular, the duration of the measurement and the reversal of the fluid flow greatly increase the chance of a particle partially blocking the sensing zone.
  • the present inventors have appreciated that this method has the disadvantage that the geometry and zeta potential of the sensing pore must be precisely known, must be invariant during analysis, and able to be modelled.
  • the geometry of the pore is assumed to be perfectly conical, and calculations are based on that assumption.
  • the present inventors have appreciated that in practice pores are typically not conical, and in many cases are not even rotationally symmetrical.
  • the method described by Kozak et al. requires that the precise geometry and dimensions of a sensing pore are measured and modelled and that the pore charge is accurately known. This is commercially impractical. Simple application of the conical model described by Kozak et al.
  • a final method is based on measuring the duration of the translocation of particles through a nanopore as a function of applied voltage.
  • Embodiments of the invention overcome or at least mitigate at least some of the problems associated with existing methods by providing a method for the measurement of particle surface charge that: enables particle by particle charge measurements; is able to measure a large number of particles; is not limited by requirements of measuring the system geometry at a high precision prior to analysis; includes a consideration of convection and electroosmosis in its theoretical approach; and incorporates a differential pressure across the nanopore that can be used to slow down the translocation Of particles, allowing better resolution of the blockade shape for each particle, which is particularly useful for accurate calibration of the nanopore with particles of a known Zeta Potential.
  • the present invention provides a method of using the size and shape of a signal generated by individual objects travelling through a resistive pulse sensor of either known or unknown geometry, for example a nanopore or micropore (or, more generally, an aperture), to measure their relative electrophoretic mobility.
  • a resistive pulse sensor of either known or unknown geometry, for example a nanopore or micropore (or, more generally, an aperture)
  • the surface charge density and Zeta Potential of each object can be calculated by calibrating the resistive pulse sensor using particles of defined surface charge density or Zeta Potential respectively.
  • the objects passing through the pore for analysis can consist of any material including solids (e.g. carbon, silica, polymers, metals), biological particles (e.g. viruses, bacteria, microvesicles, exosomes, liposomes, cells), liquids (e,g. emulsions) or gases (e.g. nanobubbles).
  • solid calibration particles e.g. carboxylated polystyrene
  • Objects passing through the pore are therefore referred to as "particles" below.
  • blockade When each particle passes through the pore, there is a resultant resistive pulse or "blockade".
  • blockade For objects with a small aspect ratio (largely spherical), the general shape of any given blockade is determined by the shape of the pore - this general shape is "stretched” in magnitude (height) and duration (width) depending on the size and the velocity of each particle.
  • the difference in particle size can be eliminated from the charge analysis calculations.
  • the proportional blockade magnitude is equal for any given particles, those particles are at the same position in the pore (or at least are assumed to be at the same position).
  • the relative velocity of those particles can therefore be directly derived by comparing the time it has taken for the particles to get to that point from any consistent defined point on the blockade pulse.
  • Electrophoresis - the particle charge will cause the particles to move through the surrounding fluid towards the oppositely charged electrode
  • Electro-osmosis the surface charge of the pore membrane (typically negative) attracts a higher density of oppositely charged (typically positive) ions to be present in the vicinity of the pore. These positive ions move towards the negative electrode and carry water molecules with them to create a "plug flow" of fluid.
  • the electrophoresis component will vary between particles on the basis Of surface charge.
  • the present invention provides a method of resolving particle velocity into these three components and deriving the surface charge of an unknown particle by comparing the measured electrophoretic velocity with that of a calibration particle with known surface charge.
  • the effective particle position within the sensor will be the same when the relative blockade magnitude is the same.
  • the measured velocity along with the known convective and electro-osmotic components derived from calibration particles, are used to calculate electrophoretic velocity of the measured particle.
  • the particle surface charge (zeta potential) is then calculated by comparison of this measured electrophoretic velocity with the calibration particles of known surface charge (zeta potential).
  • the strength of this novel method is in its simplicity.
  • the method does not require any prior knowledge of the geometry of the sensor, which is prohibitively expensive and time-consuming to measure on a commercial basis (using electron microscopy or similar).
  • the relative electrophoretic velocity of each individual unknown object is simply calibrated against a known particle set based purely on resistive pulse magnitude and shape, with minimal time and processing power required.
  • the objects to be measured are suspended in an electrolyte, at a concentration that allows multiple objects to be measured (ideally over a period of a few minutes for operator convenience).
  • the objects to be measured are smaller than the sensing area to avoid blockages.
  • Sampling frequency of the current is sufficiently fast to capture a number of data points on each pulse. If sampling frequency is too slow for a particular setup, pulses can be slowed down by application of a pressure differential across the pore or adjustment (even reversal) of the applied bias voltage.
  • Electrophoresis is a significant proportion of the total forces acting on the objects being measured (in particular the calibration particles). This can normally be achieved by increasing bias voltage and reducing pressure differential.
  • the pore zeta potential can change and affect electroosmosis.
  • the pore zeta potential is evaluated in order to accurately measure particle zeta- potentials.
  • Pore zeta potentials can be determined in situ via streaming potential measurements using variable external pressure applied to the pore. The movement of a liquid through a pore, by applying some variable external pressure creates a streaming potential and streaming current. The pore zetapotential is calculated from the streaming potential vs pressure slope, taking into account the geometry of the pore.
  • This in situ measurement of the pore zeta potential is useful when chemical and/or biological reactions are monitored in resistive pulse sensors.
  • Different biological systems can affect the pore in very different ways, and checking the Zeta potential of the pore both before and after measuring a biological sample allows these changes to be detected and quantified.
  • Another approach to compensate for this binding effect is through the addition of calibration particles (of known Zeta Potential) to the sample fluid, which will then be measured under identical conditions to the sample.
  • This method can provide an absolute surface charge measurement even if the Zeta Potential of the pore has been modified by, for example, exosomes, liposomes, proteins, aptamers, DNA, RNA or any other agents.
  • An advantage of this approach is that if the pore characteristics change during, and/or as a result ⁇ the analysis the calibration particles can be used to account for the change through the course of the analysis and provide correct sample measurements. This method can be enhanced through the addition of multiple calibration particle sets each of different known Zeta potentials.
  • a further approach to treating problems associated with the binding effects is to prevent binding through surface treatment of the pore.
  • This can consist of permanently coating the pore surface with an anti-fouling agent.
  • the treatment can involve adding a "blocking agent" to the pore just prior to measurements, which binds to all of the available attachment sites on the surface of the pore and gives a known stable Zeta Potential for the duration of the calibration and sample measurements.
  • a blocking agent is that the blocking agent can be matched to accommodate different sample particle types and carrier fluids.
  • Figure 1 is a schematic comparison of the blockade shapes resulting from a larger and smaller particle travelling at the same speed, for a generally conical aperture.
  • Figure 2 is a schematic comparison of the blockade shapes resulting from a larger and smaller particle travelling at the same speed, for a different aperture shape.
  • Figure 3 is a plot of Average (Vx)tot (i.e., 1 Tx) against bias voltage Vfor calibration particles (Example 1).
  • Figure 4 is a plot of Calculated (Vx)c as a function of % of dR max for calibration particles, from 10% to 40% of dR max (Example 1).
  • Figure 5 is a plot of zeta potential vs size for multiple applied pressures, showing repeatable results.
  • Figure 6 is a plot of zeta potential vs size for multiple applied bias voltages, showing repeatable results.
  • Figure 7 is a plot of zeta potential vs size for highly charged (Carboxylated) and less charged (Plain) PS particles.
  • Figure 8 is a plot of zeta potential vs size illustrating the detection of the surface modification of liposomes via detection of a change in zeta potential.
  • Figure 9 is a plot of zeta potential vs size illustrating the measurement of a suspension of liposomes "spiked" with carboxylated calibration particles.
  • a nanopore or micropore of fixed or variable geometry formed in an impermeable membrane.
  • the exact geometry and dimensions of this pore may be known but typically the exact geometry and dimensions of the pore would be unknown.
  • the membrane is fitted into apparatus which allows a well (or reservoir or chamber) of electrolyte to be placed on either side of the membrane - the wells are connected to each other only through the pore itself.
  • the aperture or pore may be provided as a (small) hole in a sheet, the sheet forming (part of) a wall between the two chambers and thereby separating the chambers from each other.
  • the apparatus contains at least one electrode in contact with each of the electrolyte wells such that a user defined bias voltage can be applied across the pore and the resulting electric current through the pore can be monitored.
  • a user defined electric current may instead be applied through the pore and the resulting voltage across the pore may be monitored.
  • the apparatus includes a means to vary the pressure applied to either one or both of the electrolyte wells such that a user defined differential pressure (Pap) can be applied in either direction across the pore, resulting in a convective flow of electrolyte from one well to the other or vice versa.
  • a user defined differential pressure Pap
  • the objects passing through the pore for analysis can consist of any material including solids (e.g. carbon, silica, polymers, metals), biological particles (e.g. viruses, bacteria, microvesicles, liposomes, cells), liquids (e,g. emulsions) or gases (e.g. nanobubbles).
  • solid calibration particles e.g. carboxylated polystyrene
  • Objects passing through the pore are therefore referred to as "particles" below.
  • the method allows for quantitative measurement of chemical/ biochemical reactions on particle surfaces that alter particle zeta potential.
  • the capacity to detect such changes in particle zeta potential forms the basis of pore based diagnostic assays.
  • Surface reactions may include the specific binding of aptamers, proteins, antibodies, lectins, DNA, RNA, other chemical or biochemical reagents to the surface of the particle.
  • the particle may include cells, extracellular vesicles, subcellular complexes, liposomes, synthetic particles, but not limited to these.
  • the reaction may be quantified by comparative measurement of particle zeta potential before and after incubation of the particle with the surface modifier for a period of time under appropriate conditions or the reaction process may be monitored continuously in real time.
  • blockade For objects with a small aspect ratio (largely spherical), the general shape of any given blockade is determined by the shape of the pore; this general shape is “stretched” in magnitude (height) and duration (width) depending on the size and the speed of each particle.
  • Figure 1 illustrates the passage of a larger particle (top half of Figure 1) and a smaller particle (bottom half of Figure 1) travelling through a pore at the same speed, with corresponding plots of electrical resistance against time showing the resulting blockade shapes.
  • the method identifies the point of greatest resistance in the signal trace (the blockade peak), which in the preferred pore setup is close to the beginning of the blockade.
  • the time at which the peak occurs is defined as tioo (time at 100% of peak magnitude) and the maximum magnitude of the pulse (relative to the local baseline resistance) is recorded as dR max.
  • the blockade is divided into "n" sections, and the duration from tioo is recorded for each section.
  • n 4 sections: 40%, 30%, 20% and 10% of dR max.
  • the duration from tioo to each of these sections is defined at Uo, t3o, t2o and tio.
  • Electrophoresis - the particle charge will cause the particles to move through the surrounding fluid towards the oppositely charged electrode
  • Electro-osmosis the surface charge of the pore membrane (typically negative) attracts a higher density of oppositely charged (typically positive) ions to be present in the vicinity of the pore. These positive ions move towards the negative electrode and carry water molecules with them to create a "plug flow" of fluid.
  • the magnitude of the convection component increases linearly with applied pressure, and the magnitudes of the electrical components increase linearly with applied voltage.
  • Electrophoresis and electro-osmosis are opposing forces if the particle charge (Zeta Potential " ⁇ ⁇ ”) has the same polarity as the membrane charge (Zeta Potential Their relative velocity components per mV of Zeta Potential are equal and opposite, so if the Zeta Potential of both the particle and the pore are known (as is the case when using calibration particles), the velocity components can be simplified to two:
  • this equation can be applied at any given reference point x in the pore - for the simple worked example the surface charge of the particle is calculated at each of the four reference points Uo, t3o, t2o, and tio and the answers are averaged. More advanced analysis methods can be applied to improve the data quality, as detailed below.
  • Equation D The inverse times 1/T X are averaged over N calibration particles (typically 200), as shown in Equation D.
  • T x being the duration the particle i takes, from entering the pore to the position x within the pore.
  • Equation E also applies for v e and v c and hence Equation F applies: Equation F:
  • Quantifying the convection component v c in Equation F will leave an electrical component v e , that can be used to calculate the surface charge density and zeta potential of the particle.
  • Charged calibration particles of closely controlled diameter and known Zeta Potential ⁇ ⁇ are typically used to calibrate the pore.
  • (Vx) c of the calibration is determined by measuring the calibration at various pressures and plotting (VjJ, ot vs pressure.
  • the slope of the ( ⁇ ) ⁇ vs P linear curve is proportional to the relative convective velocity per unit pressure vf which is defined as:
  • Pi is the inherent pressure head (a known constant for any given equipment setup) and P ap the applied pressure.
  • vf can be used to calculate the convection velocity (v ⁇ c at any pressure or vacuum setting P a p-(Vx c and (vj e can be either determined together (by calculating one and subtracting that from (Vx)tot to determine the other) or calculated independently by application of a number of pressures and voltages (by plotting 1/ X vs P and 1/T X vs
  • V V
  • the latter method may give better measurement repeatability when sample and calibration particles are analysed over a wide range of pressures and voltages.
  • by calculating the two components separately it is possible to more accurately assess the velocity component when it is dominant, and similarly with the electrical component.
  • the value calculated for the other component may be less accurate. If the settings (voltage and pressure) are adjusted to make one force (convection or electrical force) dominant over the other, then it is possible to calculate that force and corresponding velocity component more accurately.
  • the settings can then be adjusted to make the other force dominant, to more accurately calculate that other force and corresponding velocity component.
  • This method may avoid the magnification of measurement errors of the non-dominant component as the relative contribution of the forces varies.
  • the convection velocity component may make up only a small fraction of the total velocity at the voltage sweep calibration settings, so large errors may be present in the calculated convective velocity per unit pressure.
  • a large pressure or vacuum is applied that error may be greatly magnified. Therefore, measurements may be taken at a second pressure value, and the flow per unit pressure can thus be calculated independently. This may result in a small discrepancy at the voltage sweep calibration point, but gives improved stability for applying a range of pressures and vacuums.
  • v x v can be used to calculate the theoretical (v e Ca i of the calibration particles' at any voltage V.
  • Particles with the same Zeta Potential have the same surface charge density (assuming that the Smoluchovski approximation applies - which for particles of interest in physiological buffers is typically the case), and particles with the same surface charge density have the same electrophoretic mobility under an applied voltage, independent of particle diameter.
  • Calibration particles are cleaned out of the pore and fluid wells and sample particles are analysed in the same electrolyte at the same pore stretch (for a flexible pore). Applied pressure and voltage may differ from the calibration run.
  • the convection velocity ( ⁇ ) c sample for the sample particle measurement pressure is the product of v and the net pressure (P m + Pa ) sample - (Equation G).
  • the electrical velocity of the sample particle i ( ⁇ ' ⁇ ⁇ sample is the measured (J*) tot sample minus the calculated ⁇ v' ⁇ c sample (Equation F).
  • Equation J p Sample ⁇ ⁇ net Sample " ⁇ " ⁇
  • the zeta potential of each sample particle i can be calculated from the ratio of the electrical velocities of sample and calibration (Equation I).
  • the zeta potential of each sample particle i is given by averaging respective zeta potential values, calculated at positions x. Equation K:
  • the simplest embodiment of the method analyses pre-defined points on each blockade (40% to 10% of the blockade peak magnitude dR max in the example above).
  • a particle travelling very fast will move a long way between data sampling points. It is therefore likely that the very peak of the blockade will fall between sample points and will not be correctly identified, leading to an error in the value of both dR max and tlOO.
  • An error in tlOO will generate a large percentage error in the calculated t90, for example, but a much smaller percentage error in tlO - so the trailing end of the blockade may give better quality information than the area around the peak.
  • a particle travelling slowly will not move a long way between data sampling points, so the identified blockade peak dR max and time tlOO are likely to be relatively accurate.
  • the peak dR max and the time tlOO for each sample blockade can be calculated more accurately
  • a Modifying the system electronics to allow application of a larger voltage for a given pore size.
  • b Implement algorithms that allow signal information to be extracted from within the noise floor. Such algorithms are well known in the art.
  • the principles of the method can be applied to pores of any geometry, by identifying one or more distinct features in the blockade profile that allow the relative velocities of different particles to be calculated.
  • the example in Figure 2 shows a pore with a different profile.
  • This example shows the use of calibration particles to establish v x p and v x e .
  • Measurements of the calibration particles were made at three different applied voltages; 0.4V, 0.5V, and 0.6V. The results are displayed in Figure 3 and Figure 4. The measurement details are:
  • Vx c for the calibration particles can be calculated at any of the applied voltages , for example (v ⁇ c 0 is calculated below at all three voltages:
  • This example demonstrates the measurement of particle zeta potential after deliberate surface modification to demonstrate detection of specific surface targets.
  • This example shows the binding of a protein (CD63) to a liposome that was modified to bind CD63.
  • Figure 8 shows the liposomes before and after binding of CD63. A shift in zeta potential toward a more positive value is observed upon binding of protein, which was expected as the protein is slightly positively charged in experimental conditions.
  • Figure 8 it can be seen that the liposomes before protein binding form a distinct 'group from the liposomes with surface-bound protein. This illustrates analyses that can be used to detect particular targets in the sample.
  • Figure 8 also shows a control particle set of known, negative charge, which validates the results.
  • a number of values are measured, determined, calculated or otherwise derived, as well as processed, plotted, stored or otherwise used. It will be understood that, where appropriate (and whether or not specifically mentioned) a reference to such "values" may include a reference to values derived therefrom.

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Abstract

L'invention concerne un procédé permettant de déterminer la charge d'au moins une particule de test (telle que définie présentement), lequel consiste à : appliquer l'un d'un courant et d'une tension électriques dans une ouverture reliant deux chambres, les chambres étant au moins partiellement remplies d'un électrolyte et ladite au moins particule de test étant en suspension dans l'électrolyte d'au moins une des chambres ; mesurer une valeur indiquant l'autre parmi le courant et la tension électriques dans l'ouverture ; déterminer un intervalle de temps entre un premier et un second point dans le temps, le second point dans le temps correspondant à un point dans le temps où le courant mesuré ou la tension mesurée a atteint une proportion spécifique du courant mesuré ou de la tension mesurée au premier point dans le temps ; et déterminer la charge de ladite au moins une particule en : déterminant une valeur indiquant une composante de vitesse électrique d'une vitesse totale d'au moins une particule d'étalonnage possédant une charge connue, et tenant compte du fait que la vitesse totale de ladite au moins une particule d'étalonnage comprend une composante de vitesse convective différente de zéro et la composante de vitesse électrique ; déterminer une valeur indiquant une composante de vitesse électrique d'une vitesse totale de ladite au moins une particule de test en tenant compte du fait que la vitesse totale de ladite au moins une particule de test comprend une composante de vitesse convective différente de zéro et la composante de vitesse électrique ; et utiliser les valeurs déterminées indiquant les vitesses de composantes électriques de la particule de test et de la particule d'étalonnage afin d'étalonner la relation quantitative entre la charge de ladite au moins une particule de test et l'intervalle de temps déterminé.
PCT/GB2014/000347 2013-09-03 2014-09-03 Mesure de la charge d'une particule WO2015033090A1 (fr)

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